Gas welding torch. Installation of welding torches. Operating principle of an injection burner Drawing of an injection burner

Gas welding is welding using molten metal. During this process, the edges of the metal parts of the parts are heated to the melting point by the flame of a gas burner.

The high temperature at which the metal melts occurs from the ignition of the gas-oxygen mixture. Melted filler wire is used to fill the voids that occur when the edges of the metal meet.

Torches for gas welding.

To obtain the welding flame necessary for working with metals, a torch is used. With its help, you can control the power and volume of the flame within established limits. Despite all the external simplicity of the product, the torch is a complex and significant element in welding.

Figure No. 1 shows a gas burner flame with temperature indicators.

According to their design, gas welding torches are divided into:

• injection;
• non-injector.

According to the fuel used:

• acetylene;
• for other gases and liquid fuels.

The order of use may be:

• manual,
• by machine.

Injector and non-injector torches for gas welding.

The structural presence of a jet pump in the burner is determined by the pressure level at which fuel is supplied to it. If it is high, then no additional injection is required; the fuel is supplied under its own power. At low pressure, more gas is needed, so forced supply using an injector is used. To create a welding flame, you need to obtain a high-quality mixture of oxygen and fuel in the mixing chamber of the torch.

A burner without an injector has a simpler design. Fuel and oxygen are supplied to the mixer simultaneously using a supply system consisting of hoses, the required number of taps (valves), and nipples. A homogeneous mixture is formed in the mixer.

The homogeneous mixture flows through the tip tube to the mouthpiece, ignites and creates a flame for welding. In order for the combustion process to meet the necessary requirements, the pressure with which the mixture is supplied from the mouthpiece must be within strictly defined limits. If the speed is higher than the set speed, the flame, breaking away from the burner cut, will go out. If it is lower, then the mixture, getting inside the burner, will explode in it. The supply speed of the flammable mixture (acetylene-oxygen) varies from 70 to 160 m/sec, it depends on the type of mouthpiece, the size of the channel, and the percentage composition of the mixture.

High pressure burners can use hydrogen or methane. It is easy to use and easy to set up. But, in comparison with low pressure injection burners, they are used much less frequently.

Low pressure burner operation.

Oxygen under high pressure (about 4 atmospheres) enters the burner through a supply system consisting of a nipple and an adjustment valve. Passes through the injector at high speed. Under the influence of a stream of oxygen, a pressure below atmospheric pressure is created in the chamber of the jet pump and flammable gas is sucked in. It enters through the nipple and valve into the injector chamber, and then into the mixing chamber, connects with oxygen, and flows through the channel to the mouthpiece at a speed within strict limits.

The oxygen consumption does not change, it is not affected by external factors, unlike the consumption of the gas used. An increase in the temperature of the mouthpiece and burner tip, a change in pressure, and an increase in resistance increase the consumption of acetylene.

Other types of burners.

In some industries, gas welding torches operating on liquid fuels such as gasoline or kerosene have been used. The principle is based on the spraying of a kerosene-oxygen mixture and the evaporation of fine-droplet fuel from heating from the mouthpiece.

For trouble-free operation, currently used burners must meet the following safety requirements:

• the welding flame must be of a certain shape;
• adjusting the flame within the required limits;
• resistance to external influences and operational safety;
• ease of use.

A welding gas torch is a specialized design in which flammable gas or vapor of a special liquid is mixed with oxygen from the environment. Thanks to this, a stable welding flame of the required power occurs. In principle, it is generally accepted that this equipment is one of the main working tools of a gas welder.

There are quite a few types of welding torches. Despite the fact that the principle of their operation is approximately the same, they may have a number of features:

• Injector and non-injector designs - they differ from each other in the technology of supplying oxygen to the combustion area;
• Gas or liquid. In the former, a special flammable gas is used to obtain a flame of the required temperature, while the latter operate on gasoline or kerosene vapor;
• Specialized or universal, the latter can be used for any work related to cutting or welding metal;
• Single-flame and multi-flame are differentiated depending on the flow of the supplied flame;
• Machine and manual;
• Gas welding torches can be classified by power: low, medium, high.

Operating principle of injectionless operation

If the welding torch operates at high pressure and has an injector, then its design will be much simpler compared to a design where the pressure is much lower. The technology of its operation is as follows:

• Oxygen enters it through special necks made of rubber, passing through the valve, and then is sent to the mixer;
• In the mixer, the entire flow is divided into many small jets and directed into the mixer nozzle. Using the same technology, it is sent to a special valve;
• The resulting mixture in MIG-MAG welding torches passes through a gas flow of a significant cross-section, where circulation ends, and at the exit it turns out to be the most homogeneous;
• On the tip tube there is a mouthpiece, which is made from durable, non-oxidizing copper. The mixture at the outlet will immediately burn completely, and the temperature will be quite high, which will be significantly higher compared to the melting point of the metal.

In order for a torch intended for gas welding, the gas flow must come out evenly at the most accurately adjusted speed, and the mixture must burn completely. If the gas exit velocity is low, then the flame can move to the upper part of the burner - this is quite dangerous, since an explosion of this mixture often occurs inside the burner.

If the speed is too high, the flame will break away from the mouthpiece and move further and further from the cut, which will ultimately lead to its attenuation. To determine the required speed, it is necessary to take into account several important data: what the combustible mixture consists of, what is the internal diameter of the nozzle, how the mouthpiece is designed. It is possible to calculate the correct fuel supply rate only if all these data are known.

The average value is considered to be in the range from 70 to 160 m/s. In order to ultimately achieve a suitable output speed, a pressure of about 0.5 atmospheres will have to be created, and the pressure for gas or vapor and oxygen will be approximately the same.

Injection burners

The design of the welding torch involves the use of acetylene, hydrogen or methane as fuel, and it is very easy to use. The principle of operation is as follows: oxygen from the cylinder enters through a special valve, passing through the injector cone, and enters the mixing chamber. A flammable gas is pumped through the injector and intensively mixed with oxygen. After this, the formed mixture is sent through the tip tube into the mouthpiece. Thanks largely to oxygen, the pressure of the gas escaping from the mouthpiece nozzle becomes significantly less than atmospheric pressure.

However, for high-quality combustion and obtaining a normal temperature, it must be at least 3.5 atmospheres. It is worth noting that the injection burner has one very serious drawback: the composition of the combustible mixture remains variable, which does not allow for high-quality and constant combustion.

Despite the fact that this product operates at low pressures, it is used much more often than designs designed for high pressure. The structure of this product is somewhat more complicated, since it contains a special cooling unit for the welding torch. The fact is that low pressure causes quite strong heating of the nozzle and other elements. The main thing here is to prevent the chamber where the flammable mixture is formed from overheating and exploding.

Features of welding work using a gas torch

First of all, gas torches are distinguished by the fact that they are perfect for semi-automatic or automatic welding work, when the welding wire is fed without the use of hands, which greatly facilitates the technological process.

Thanks to automatic welding, you can qualitatively weld all hard-to-reach areas, and you will have to apply a minimum amount of effort. The amount of waste from such work is minimal. The weld seam is quite strong in a much shorter period of time than during electric arc welding. There are not too many disadvantages to this technology; they relate, first of all, to the rather high cost of equipment and components. The entire system is complex in terms of design; the products are very heavy and bulky, so moving them from one place to another will be very problematic.

The welding process consists of the following stages:

• The areas of the parts to be welded must be thoroughly cleaned of all traces of rust or corrosion. You can do this using a special metal brush attached to an angle grinder.
• Be sure to degrease the surface using TIG or other compounds, otherwise the consumable electrode will not adhere too tightly to the metal;
• The gas burner is activated, the semi-automatic electrode supply mechanism is started and the direct work of connecting metal elements begins;
• Be sure to set the electrode feed speed. It depends on the type of metals being welded, their thickness and a number of other factors.

How to properly handle the burner?

Before you begin the actual work, you need to check how well the injection component of the equipment works. To do this, connect the oxygen reducer hose to the nipple that supplies oxygen. Carefully raise the pressure in the system to operating pressure.

When oxygen passes through the injector, a vacuum should occur in the acetylene channel. If it is, the finger will stick to the acetylene nipple. In this case, connect both hoses and carefully secure them; only after this can the combustible mixture be ignited and the flame size adjusted.

When finishing work, first close the valve of the acetylene cylinder, and then close the oxygen valve. If you do the opposite, a fire may strike the hose through which acetylene is supplied, which can lead to an explosion. If the work technology is followed, it will be possible to obtain a reliable connection that will retain its strength for a long time.

Burners are divided into injection and non-injector, single-flame and multi-flame, for gaseous fuels (acetylene, etc.) and liquid (kerosene vapor). The most widely used are injection burners operating on a mixture of acetylene and oxygen.

Diagram and principle of operation of an injection burner. The burner consists of two main parts - the barrel and the tip (Fig. 64). The barrel has oxygen 1 and acetylene 16 nipples with tubes 3 And 15 , handle 2 , frame 4 with oxygen 5 and acetylene 14 valves. On the right side of the burner (looking in the direction of gas flow) there is an oxygen valve 5 , and on the left side there is an acetylene valve 14 . The valves are used to start, regulate the flow and stop the gas supply when the flame is extinguished. Tip consisting of an injector 13 , mixing chamber 12 and mouthpiece 7 , is attached to the burner barrel body with a union nut.

Injector 13 It is a cylindrical part with a central channel of small diameter for oxygen and peripheral, radially located channels for acetylene. The injector is screwed into the mixing chamber of the tip and is located in the assembled burner between the mixing chamber and the gas supply channels of the burner body. Its purpose is to create a rarefied state with an oxygen stream and suck in acetylene supplied under a pressure of at least 0.01 kgf/cm 2 . The vacuum behind the injector is achieved due to the high speed (about 300 m/s) of the oxygen jet. The pressure of oxygen entering through valve 5 ranges from 0.5 to 4 kgf/cm 2 .

The injection device is shown in Fig. 65.

In the mixing chamber, oxygen is mixed with acetylene and the mixture enters the mouthpiece channel. The flammable mixture leaving the mouthpiece at a speed of 100 - 140 m/s burns when ignited, forming an acetylene-oxygen flame with a temperature of up to 3150°C.

The torch kit includes several tip numbers. For each tip number, the dimensions of the injector channels and the dimensions of the mouthpiece are established. In accordance with this, the consumption of oxygen and acetylene during welding changes.

The design of propane-butane-oxygen burners differs from acetylene-oxygen burners in that there is a device in front of the mouthpiece 10 (Fig. 64) for heating the propane-butane-oxygen mixture. Additional heating is necessary to increase the flame temperature. The regular mouthpiece is replaced by a modified mouthpiece design.

Technical characteristics of injection burners. Currently, the industry produces welding torches of medium power - "Zvezda", GS-3 and low power - "Zvezdochka" and GS-2. The “Moscow” and “Malyutka” burners, produced before 1971, are also in operation.

Torches "Moscow", "Zvezda" and GS-3 are designed for manual oxy-acetylene welding of steel with a thickness of 0.5 - 30 mm.

The medium-power torch kit includes a barrel and seven tips attached to the torch barrel with a union nut (Table 15). The required set includes tips No. 3, 4 and 6, most often necessary when performing welding work, the remaining tips are supplied at the request of the consumer. Burners "Zvezdochka", GS-2 and "Malyutka" are supplied with tips No. 0, 1, 2, 3. In burners "Zvezda", GS-3, "Zvezdochka" the mouthpieces are made of bronze Br.Kh 0.5, metal more more resistant than MZ copper, which was used for the manufacture of mouthpieces for “Moscow” and “Malyutka” burners. For this reason, the service life of the burners produced is increased compared to those produced previously.

Burners of the GS-3 type work with hoses with a diameter of 9 mm. Low-power torches "Malyutka", "Zvezdochka" and GS-2 are designed for welding steels with a thickness of 0.2 - 4 mm. GS-2 burners work with rubber hoses with a diameter of 6 mm.

For the propane-butane-oxygen mixture, the industry produces burners of the GZU-2-62-I and GZU-2-62-II types; the first is intended for welding steel with a thickness of 0.5 to 7 mm, the second is for heating the metal. For flame cleaning of metal surfaces from rust, old paint, etc., an oxygen-acetylene torch GAO (acetylene burner, cleaning) is produced. The width of the surface processed by the burner in one pass is 100 mm.

For metal hardening, NAZ-58 tips are produced for the GS-3 burner barrel.

Welding and other types of metal processing with a propane-butane-oxygen flame can be performed with a GZM-2-62M torch with four tips.

Malfunction of the injection device leads to backfire and a decrease in the supply of acetylene in the combustible mixture. The acetylene reserve is an increase in its flow rate when the acetylene valve of the burner is fully open compared to the nominal flow rate for a given mouthpiece number. The causes of these problems may be clogging of the oxygen channel, excessive increase in its diameter due to wear of the acetylene channels, displacement of the injector relative to the mixing chamber, and external damage to the injector. For normal operation of the burner, the diameter of the outlet channel of the mouthpiece must be equal to the diameter of the channel of the mixing chamber, and the diameter of the injector channel must be 3 times smaller.

The injector seat is adjusted for the injectors included in the burner kit.

Injectors from the Moscow burner can be used in the Zvezda burner, and injectors from the Malyutka burner can be used in the Zvezdochka burner.

The burner is checked for injection (vacuum) every time before starting work and when changing the tip. To do this, remove the acetylene sleeve from the nipple and open the oxygen valve. A suction should be created in the acetylene nipple of a working burner, which can be detected by touching the nipple hole with a finger.

Maintaining the mouthpiece in proper condition ensures a normal flame in shape and size (see Chapter X). Mouthpieces operate at high temperatures, are subject to mechanical destruction from welding spatter and require maintenance (cleaning, cooling, etc.). Scores, scuffs, and carbon deposits on the walls of the outlet channel of the mouthpiece reduce the rate of release of the combustible mixture and contribute to the formation of pops and backfires, distorting the shape of the flame. These shortcomings are eliminated by trimming the end of the mouthpiece by 0.5 - 1 mm, calibrating and polishing the outlet hole.

After each repair, burner parts must be degreased with B-70 gasoline.

Injectorless burners operate under the same pressure of oxygen and acetylene, equal to 0.1 to 0.8 kgf/cm2. These burners provide a more constant composition of the combustible mixture during operation. Non-injector burners can be powered with acetylene, either from cylinders or from medium pressure generators.

Special burners. For gas-flame processing of materials, it is sometimes advisable to use special burners. The industry produces burners for heating metal for the purpose of heat treatment, removing paint, rust, burners for soldering, welding thermoplastics; flame surfacing, etc. The fundamental design of special torches is in many ways similar to the torch used for welding metals. The difference lies in the shape and size of the mouthpieces, as well as in the heat output, shape and size of the flame. Special burners are produced for any flammable gas.

Control questions

1. Why is acetylene mainly used for gas welding from flammable gases?

2. Tell us about the classification of acetylene generators.

3. What role does the injector play in the burner?

4. What effect does the injection device and mouthpiece design have on the operation of the burner?

5. What types of special burners are there?

Burners in which the formation of a gas-air mixture occurs due to the energy of a gas stream are called injection. The main element of an injection burner is the injector, which sucks air from the surrounding space into the burners.

Depending on the amount of injected air, burners can be with incomplete air injection and with complete pre-mixing of gas with air.

Burners with incomplete air injection. Only part of the air necessary for combustion enters the combustion front; the rest of the air comes from the surrounding space. Such burners operate at low gas pressure. They are called low-pressure injection burners (Fig. 3, a).

The main parts of injection burners are the primary air regulator, nozzle, mixer and manifold (see Fig. 3).

Rice. 3. Injection atmospheric gas burners:

a - low pressure; b - burner for a cast iron boiler; 1 - nozzle; 2 - injector; 3 - confuser; 4 - diffuser; 5 - collector; 6 - holes; 7 - primary air regulator

The primary air regulator 7 is a rotating disk or washer and regulates the amount of primary air entering the burner. Nozzle 1 is used to convert the potential energy of gas pressure into kinetic energy, i.e., to give the gas stream such a speed that ensures the suction of the necessary air. The burner mixer consists of three parts: injector, confuser and diffuser. Injector 2 creates a vacuum and air leaks. The narrowest part of the mixer is confuser 3, which levels the stream of the gas-air mixture. In diffuser 4, final mixing of the gas-air mixture and an increase in its pressure occurs due to a decrease in speed.

From the diffuser, the gas-air mixture enters the manifold 5, which distributes it among the holes 6. The shape of the manifold and the location of the holes depend on the type of burners and their purpose.

The distribution manifold of the burners of cylinder water heaters has the shape of a circle; for the burners of instantaneous water heaters, the manifold consists of parallel tubes; for units with an elongated firebox, the manifold is elongated; burners for a cast iron boiler (Fig. 3, b) have a rectangular collector with a large number of small holes.

Low-pressure injection burners have a number of positive qualities, due to which they are used in household gas appliances, as well as in gas appliances for catering establishments and other household gas consumers. Injection burners are also used in cast iron heating boilers.

The main advantages of low-pressure injection burners: simplicity of design, stable operation of burners when loads change; reliability and ease of maintenance; quiet operation; possibility of complete combustion of gas and operation at low gas pressures; lack of pressurized air supply.

An important characteristic of incomplete mixing injection burners is the injection coefficient - the ratio of the volume of injected air to the volume of air required for complete combustion of the gas. So, if 10 m3 of air is needed for complete combustion of 1 m3 of gas, and the primary air is 4 m3, then the injection coefficient is 4: 10 = 0.4.

A characteristic of burners is also the injection ratio - the ratio of primary air to burner gas flow. In this case, when 4 m3 of air is injected per 1 m3 of burned gas, the injection ratio is 4.

The advantage of injection burners is their self-regulating property, i.e. maintaining a constant proportion between the amount of gas supplied to the burner and the amount of injected air at a constant gas pressure.

The limits of stable operation of injection burners are limited by the possibilities of flame separation and breakthrough. This means that it is possible to increase or decrease the gas pressure in front of the burner only within certain limits.

Burners with complete pre-mixing of gas and air. The injection of all the air required for complete combustion of the gas is ensured by increased gas pressure. Full gas mixing burners operate in the pressure range from 5000 Pa to 0.5 MPa. They are called medium-pressure injection burners and are used mainly in heating boilers and for heating industrial furnaces. The thermal power of burners usually does not exceed 2 MW. The main difficulties in increasing their power are the difficulty of combating flame breakthrough and the bulkiness of the mixers.

These burners produce a low-luminous torch, which reduces the amount of radiation heat transferred to heated surfaces. To increase the amount of radiation heat, it is effective to use solid bodies in the furnaces of boilers and furnaces, which perceive heat from combustion products and radiate it to heat-receiving surfaces. These bodies are called secondary emitters. Fireproof walls of tunnels, walls of furnaces, as well as special perforated partitions installed in the path of movement of combustion products are used as secondary emitters.

Burners with complete pre-mixing of gas and air are divided into two types: with metal stabilizers and refractory nozzles.

The injection burner designed by Kazantsev (IGK) consists of a primary air regulator, a nozzle, a confuser, a mixer, a nozzle and a plate stabilizer (Fig. 4).

Rice. 4. IGK injection burner:

1 - stabilizer; 2 - nozzles; 3 - confuser; 4 - nozzle; 5 - primary air regulator

The primary air regulator 5 of the burner simultaneously functions as a noise muffler, which is created due to the increased speeds of the gas-air mixture. Plate stabilizer and flame breakthrough in a wide range 7 ensures stable operation of the burner without flame separation or breakthrough in a wide range of loads. The stabilizer consists of steel plates 0.5 mm thick with a distance between them of 1.5 mm. The stabilizer plates are pulled together by steel rods, which create a zone of reverse flows of hot combustion products along the path of the gas-air mixture and continuously ignite the gas-air mixture.

In burners with refractory nozzles, natural gas burns to form a low-luminous flame. In this regard, the transfer of heat by radiation from the burning gas torch is insufficient. Modern gas burner designs have significantly improved gas efficiency. The low luminosity of the gas torch is compensated by the radiation of hot refractory materials when burning gas using the flameless combustion method.

The gas-air mixture in these burners is prepared with a slight excess of air and enters hot refractory channels, where it heats up intensively and burns. The flame does not come out of the channel, therefore this gas combustion process is called flameless. This name is conditional, since there is a flame in the channels.

The gas-air mixture is heated from the hot walls of the channel. In places where channels expand and near poorly bluffed bodies, retention zones of hot combustion products are created. Such zones are stable sources of constant heating and ignition of the gas-air mixture. In Fig. Figure 5 shows a flameless panel burner. The gas entering the nozzle 5 from the gas pipeline 7 injects the required amount of air, regulated by the primary air regulator 6. The resulting gas-air mixture through the injector 4 enters the distribution chamber 3, passes through the nipples 2 and enters the ceramic tunnels 1. In these tunnels, the gas-air mixture is burned. The distribution chamber 3 from the ceramic prisms 8 is thermally insulated with a layer of diatomaceous earth, which reduces heat removal from the reaction zone.

Flameless combustion of gas has the following advantages: complete combustion of gas; possibility of gas combustion with small excess air; the ability to achieve high combustion temperatures; combustion of gas with high thermal stress of combustion volume; transfer of a significant amount of heat by infrared rays.

Based on the design of their fire part, existing designs of flameless burners with refractory nozzles are divided into burners with nozzles having channels of irregular geometric shape; burners with nozzles having channels of regular geometric shape; burners in which the flame is stabilized on the fireproof surfaces of the firebox.

Rice. 5. Flameless panel burner:

1 - tunnel; 2 - nipple; 3 - distribution chamber; 4 - injector; 5 - nozzle; 6 - air regulator; 7 - gas pipeline; 8 - ceramic prisms

The most common are burners with nozzles of regular geometric shape. The refractory nozzles of such burners consist of ceramic tiles measuring 65 x 45 x 12 mm. Flameless burners are also called infrared burners.

All bodies are sources of thermal radiation arising due to the vibrational motion of atoms. During radiation, the thermal energy of substances is converted into the energy of electromagnetic waves, which propagate from the source at a speed equal to the speed of light. These electromagnetic waves, propagating in the surrounding space, collide with various objects and are easily converted into thermal energy. Its value depends on the temperature of the radiating bodies. Each temperature corresponds to a certain range of wavelengths emitted by the body. In this case, heat transfer by radiation occurs in the infrared region of the spectrum, and burners operating on this principle are called infrared burners (Fig. 6).

Through nozzle 4 (see Fig. 6, a) the gas enters the burner and injects all the air necessary for complete combustion of the gas. From the burner, the gas-air mixture enters the collection chamber 6 and is then directed into the fire holes of the ceramic tile 2. To avoid flame breakthrough, the diameter of the fire holes must be less than a critical value and be 1.5 mm. The gas-air mixture leaving the fire chambers is ignited at a low speed of its exit in order to avoid flame separation. In the future, the rate of exit of the gas-air mixture can be increased (open the tap completely), since the ceramic tiles heat up to 1000°C and give up some of the heat to the gas-air mixture, which leads to an increase in the speed of flame propagation and prevention of its separation.

Rice. 6. Infrared burners:

a - burner diagram: 1 - reflector; 2 - ceramic tiles; 3 - mixer; 4 - nozzle; 5 - body; 6 - collection chamber; b, c and d - burners GII-1, GII-8 and PS-1-38, respectively

Ceramic tiles have about 600 cylindrical fire channels, which makes up about 40% of the surface of the tiles.

The tiles are connected to each other with a special putty consisting of a mixture of fireclay powder and cement.

If infrared burners operate on medium pressure gas, then special plates made of porous heat-resistant materials are used. Instead of cylindrical channels, they have narrow curved channels that end in expanding combustion chambers.

When gas is burned in numerous channels of various nozzles, their outer surfaces are heated to a temperature of about 1000 °C. As a result, surfaces acquire an orange-red color and become sources of infrared rays, which are absorbed by various objects and cause them to heat up.

In Fig. 6, b... d shows the most common types of infrared burners. GII-1 burners have 21 ceramic tiles, a reflector and a distribution box. Using GII burners you can heat rooms and various equipment. Burners are also used for heating open areas (sports grounds, cafes, summer premises, etc.).

The GK-1-38 burner is successfully used for heating walls and plaster under construction, and heating people working in winter conditions. The burner can operate on natural and liquefied gases.